1. Technical Field
This invention relates generally to communication systems and more particularly to power amplifiers used in transmitters within such communication systems.
2. Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Communication systems typically operate in accordance with one or more communication standards. For instance, wired communication systems may operate according to one or more versions of the Ethernet standard, the System Packet Interface (SPI) standard, or various other standards. Wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. Each wireless communication device participating in wireless communications includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more frequency conversion stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with the particular wireless communication standard. The one or more frequency conversion stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As compared/contrasted to the wireless communication device described above, a transmitter of a wired communication device includes a data modulation stage, the power amplifier and may include a frequency conversion stage that frequency converts a baseband signal produced by the data modulation stage to a transmit band. While power amplifiers of wired communication devices do not typically operate in the RF range, they have similar operational requirements. In both wired and wireless communication devices, the power amplifier is often required to provide a high swing at its output. The power amplifier must also be very linear in its operation and also use as little power as possible. These competing goals are very difficult to meet, particularly in portable devices that are battery powered and that operate at relatively low voltages.